Risperidone

BRAND NAMES

Risperidone is marketed under multiple brand names, with Risperdal® being the most common in the United States. Other U.S. brands and formulations include:

• Okedi® – extended-release subcutaneous injection

• Perseris® – extended-release subcutaneous injection

• Risperdal® – oral tablet and oral solution

• Risperdal Consta® – long-acting intramuscular injection

• Risperdal M-TAB® – orally disintegrating tablet

• Risvan® – extended-release intramuscular injection

MECHANISM OF ACTION

Risperidone is an atypical antipsychotic that works by blocking dopamine D₂ and serotonin 5-HT₂ receptors in the brain. This reduces overactivity of neurotransmitters that contribute to psychotic symptoms, mood instability, and irritability. By modulating both dopamine and serotonin pathways, risperidone helps improve cognition, behavior, and emotional regulation. Its dual receptor activity accounts for a lower risk of motor side effects compared to older antipsychotics. The drug’s effect is gradual and depends on dose and treatment duration.

PHARMACOKINETICS:

Absorption: Risperidone is well absorbed after oral administration, reaching peak plasma levels in 1–2 hours for solution or tablets.

Distribution: It is widely distributed in the body and binds about 90% to plasma proteins.

Metabolism: Primarily metabolized in the liver by CYP2D6 to an active metabolite, 9-hydroxyrisperidone, which contributes to therapeutic effects.

Excretion: Excreted mainly through urine (as metabolites) and feces; half-life ranges from 3 to 20 hours depending on formulation.

PHARMACODYNAMICS

Risperidone exerts its therapeutic effects by balancing dopamine and serotonin activity in the brain. This reduces psychotic symptoms, aggression, irritability, and mood instability. Its antagonism at D₂ receptors in the mesolimbic pathway controls positive symptoms of schizophrenia. Serotonin 5-HT₂ receptor antagonism improves negative symptoms and mood regulation. Effects on other receptors, like alpha-adrenergic and histamine H₁, contribute to sedation and weight gain.

ADMINISTRATION

Risperidone can be given orally as tablets, orally disintegrating tablets, or solution, or as a long-acting intramuscular injection. Oral forms are typically taken once or twice daily, with or without food. The injectable form (Risperdal Consta) is administered every two weeks for maintenance therapy. Doses should be individualized based on the patient’s age, weight, and clinical response. Regular monitoring is recommended to optimize safety and efficacy.

DOSAGE AND STRENGTH

• Schizophrenia: Treats symptoms in adults and adolescents aged 13 and older.

• Bipolar Disorder: Manages acute manic or mixed episodes in adults and children aged 10 and older.

• Autism: Controls irritability, aggression, and self-injurious behavior in children and adolescents aged 5 to 16.

DRUG INTERACTIONS

Risperidone may interact with CYP2D6 inhibitors such as fluoxetine or paroxetine, which can increase blood levels. Other antipsychotics, antihypertensives, and drugs that prolong the QT interval may also interact. Concomitant use may require dose adjustment or closer monitoring. Alcohol may exacerbate sedative effects. Patients should always inform healthcare providers about all medications they are taking.

FOOD INTERACTIONS

• Food does not significantly affect absorption

• risperidone can be taken with or without meals.

CONTRAINDICATIONS

Risperidone is contraindicated in individuals with hypersensitivity to risperidone or its components. Caution is advised in patients with severe cardiovascular disorders, hepatic or renal impairment, or a history of seizures. It should not be used in elderly patients with dementia-related psychosis due to increased risk of cerebrovascular events. Pregnancy and breastfeeding require careful risk-benefit evaluation. Close monitoring is recommended in all high-risk populations.

SIDE EFFECTS

• Fatigue and drowsiness – feeling unusually tired or sleepy

• Weight changes – weight gain and increased appetite

• Headaches – mild to moderate head pain

• Movement-related issues – tremors, restlessness, muscle stiffness, or shuffling walk

• Dizziness or lightheadedness – especially when standing quickly (orthostatic hypotension)

• Digestive problems – nausea, vomiting, constipation, stomach discomfort, or dry mouth

• Hormonal effects – elevated prolactin causing breast swelling, unexpected milk production, irregular periods, or sexual function changes

• Sleep disturbances – difficulty falling or staying asleep (insomnia)

• Respiratory symptoms – sore throat, nasal congestion, or cold-like symptoms

OVER DOSE

Symptoms of overdose may include severe drowsiness, hypotension, tachycardia, extrapyramidal symptoms, or coma. Management is primarily supportive, including monitoring of cardiovascular and neurological status. Activated charcoal may be considered if the ingestion is recent. Hospitalization may be required for severe cases. Close observation and symptomatic treatment are critical for recovery.

TOXICITY

Risperidone has a wide therapeutic index, but excessive doses can lead to serious cardiovascular, neurological, and metabolic complications. Chronic overdose may increase the risk of tardive dyskinesia or extrapyramidal symptoms. Prompt medical intervention is essential in suspected toxicity. Monitoring and dose adjustment help prevent adverse effects. Supportive care remains the mainstay of treatment for toxic reactions.